The difficulty is much more than the common and well-known one of attending to two things at once. It is especially due,to the fact that the elementary operations of the mind are exceedingly faint and evanescent, and that it requires the utmost painstaking to watch them properly My method consists in allowing the mind to play freely for a very brief period, until a couple or so of ideas have passed through it, and then while the traces or echoes of those ideas are still lingering in the brain to turn the attention upon them with a sudden and complete reawakening; to arrest, scrutinise them, and to record their exact appearance; after

wards I collate the records at leisure, and discuss them and draw conclusions." (p. 150.)

Galton's first experiment was a leisurely walk of 450 yards down Pall Mall, on an occasion when he felt himself unusually capable of the kind of effort required. He reckoned that 300 objects caught his eye, although he never allowed his mind to ramble.

"It was impossible for ine to recall in other than the vaguest way the numerous ideas that had passed through my mind; but of this, at least I was sure, that samples of my whole life had passed before me, that many bygone incidents, which I never suspected to form part of my stock of thoughts, had been glanced at as objects too familiar to awaken the attention. I saw at once that the brain was vastly more active than I had previously believed it to be,

and I was perfectly amazed at the unexpected width of the fields of its everyday operations."

After an interval of some days in which he kept his mind from dwelling on his first experiences, Galton took a second experimental walk. He was struck as before by the variety of ideas that presented themselves, but his admiration for the activity of the mind was reduced by the observation that there was a great deal of repetition in his thought. He next devised an experiment for testing these associations and repetitions. He selected a list of 75 suitable words and sitting at a table with a stop-watch, started it on exposing a word of which he was previously ignorant. He waited till the word called up two directly associated ideas and then stopped the watch and recorded these ideas. The second associated idea was always derived from the word itself and not from the first associated idea, for he kept his attention firmly concentrated on the word itself. Sometimes he only got one associated idea ; sometimes three or four occurred together and he was able to record them, but as a rule he only managed to record two with precision. Galton went through the 75 words on four occasions at intervals of a month, "but it was a most repugnant and laborious work, and it was only by strong selfcontrol that I went through my schedule according to programme."

The total number of associated ideas was 505, and took 660 seconds to form; or at the rate of about 46 per minute or 2755 in an hour'. Of the 505 ideas, however, 29 occurred in all four trials, 36 in three, 57 in two and 107 in one trial only. Galton concluded therefore that reiterated association, even under the very different conditions of place and time of his experiments, was a much more marked feature than he had anticipated. He held from the proved number of faint and barely conscious thoughts and from the proved iteration of them, that the mind is perpetually travelling over familiar ways without the memory retaining any impression of its excursions.

"My associated ideas were for the most part due to my own unshared experiences, and the list of them would necessarily differ widely from that which another person would draw

1 There were 13 cases of "puzzle" in which nothing sufficiently definite occurred in the maximum of time, 4 seconds, allowed for each test.